1. Field of the Invention
The present invention is directed to an anesthetic apparatus of the type which is operable at least as an open system, wherein a connector for fresh gas is a part of an inspiratory section of a breathing circuit, and a bellows system and an outlet valve are part of an expiratory section of the breathing circuit. The present invention is also directed to a method for operating such an anesthetic apparatus.
2. Description of the Prior Art
Most anesthetic apparatuses are devised for operation in different modes, especially with open and closed systems.
In an open system, all the gas prepared in the anesthetic apparatus and delivered to the patient during inspiration (inhalation) is removed from the anesthetic apparatus and carried to an evacuation unit during expiration (exhalation).
In a closed system, a larger or smaller part of the gas expired by the patient is returned in the anesthetic apparatus to the patient at the next inspiration. Gas is usually returned to the patient via an absorber to remove carbon dioxide from the gas.
One problem with anesthetic apparatuses of this kind is that the compressible volumes in the breathing circuit are much larger than in apparatuses that cannot be switched between open and closed systems.
The large compressible volume in the expiratory section of the breathing circuit is a particular problem when the anesthetic apparatus operates as an open system. During inspiration, more than a negligible part of the programmed tidal volume may be consumed in compressible volume, since inspiratory pressure is greater than expiratory pressure.